Lower Lake South (Gale Island) (DNR ID: 27-0133-02)
Sampling Location - GPS Coordinates: Surface Area: 1069 acres Max. Depth: 77 ft
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Lower Lake South (Gale Island) is located near the cities of Tonka Bay and Greenwood. Head west on Minnetonka Blvd toward Maplewood Rd, and turn left to stay on Minnetonka Blvd. Next turn right to stay on Minnetonka Blvd. Public boat launch is on the right.
Lower Lake South is on Lake Minnetonka which is a class 2B lake protected for aquatic life and recreation. Water quality information is available beginning in 1974. MCWD staff have been monitoring the site on Lower Lake South on a bi-weekly basis from the time of ice out (April) to the time of fall mixing (mid-October) since 2006.
See Previous Reports.
Monitoring season started in late April and ended in late October. A YSI multi-probe sonde was used to measure dissolved oxygen (DO), temperature (oC), pH, and specific conductivity (µS/cm) at each meter depth from the water surface to the bottom. Additionally, water samples were collected within the first two meters of the surface with a 2-meter composite sampling tube. Samples one meter below the thermocline and one meter above the bottom were collected with a Van Doran water sampler. Surface samples were analyzed for total phosphorus (TP), soluble reactive phosphorus (SRP), total nitrogen (TN), where bottom and thermocline samples were analyzed for TP and SRP. Surface concentrations of chlorophyll-a were also analyzed and measurements of Secchi disc depth were recorded.
| 2009 Summer Water Quality Summary |
| Parameters | Range | Mean | TSI Value | Lake Grade |
| Months | June - Sept. | May - Sept. | ||
| Secchi Depth (m) | 2.9 - 4.1 | 3.6 | 42 | A |
| Surface TP (µg/L) | 13 - 24 | 17.8 | 46 | A |
| Chlorophyll-a (µg/L) | 1 - 6 | 4.1 | 44 | A |
| Overall Score | 44 | A |
The following summary refers to Figure 3.29 (a-d).
- From late April to late July there was an overall decline in Secchi disk depth, and then
there was a gradual increase in Secchi disk depth from early August to early October.
Secchi disk depth ranged between 2.9 m and 4.2 m (standard > 1.4 m). - Chlorophyll-a concentrations fluctuated between 4 μg/L and 5 μg/L until late July, when
concentrations declined. By early August, chlorophyll-a concentration was 1 μg/L.
Chlorophyll-a concentrations increased to 7 μg/L by early October remaining below the
standard limit (standard < 14 μg/L). - Surface TP concentrations were below the standard limit for the season (< 40 μg/L) and
fluctuated between 9 μg/L and 24 μg/L. Surface SRP were below detection limit (< 0.005
μg/L) except in early October when concentrations exceeded TP concentrations*. *Early
October SRP concentrations were greater than TP concentrations which may be due to
the presence of silica within the sample (email correspondence; RMB, 2008). - Both bottom TP and SRP concentrations increased over the season. In late June, bottom
TP concentrations declined from 349 μg/L to 257 μg/L in August and then increased to
500 μg/L in early September. Bottom SRP analysis was not performed in late September
due to inefficient sample volume upon delivery.
Lake Grades and Historical Monitoring Summaries
When available, previous reports are linked to applicable year. Additional lake data previous to 2007 may be available in the applicable year's hydrodata report. If you have additional questions or you are looking for specific information please contact MCWD's Water Quality Staff.
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